qi

A small DSL for async flow control.

npm install qi
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Qi

Pronounced 'chee'.

A simple DSL for parallel and sequential processing.

It is simpler and smaller than any other flow control library you will find, and the features are so powerful, it's probably a monad.

It supports three operations:

  • disperse
  • focus
  • channel

From these we derive more complex functions for specific use cases:

  • map
  • others?

Installation

npm install qi
bower install qi

High Level Operators

These are convenient functions for common use cases.

Map

Map over arrays or objects, executing an asynchronous function.

Example

should = require 'should'
{map} = require 'qi'

squareAsync = (n, next) ->
  next null, n * n

describe 'map', ->
  it 'should process an array', (done) ->
    map [1, 2, 3], squareAsync, (err, results) ->
      results.should.eql [1, 4, 9]
      done()

  it 'should process an object', (done) ->
    map {a: 1, b: 2, c: 3}, squareAsync, (err, results) ->
      results.should.eql {a: 1, b: 4, c: 9}
      done()

Fundamental Operators

These are the 3 base operators, from which all others are derived.

Focus

Initialize it on a target function and you will get a callback constructor. You may create as many callbacks as you want and pass them to your subtasks. The target will be called when the subtasks have completed.

It supports the node convention of (err, data). If any of your subtasks return results they will be accumulated in an array. If any return an error, the target will be called immediately with the error, and the results of all further subtasks will be ignored.

You can pass a 'name' to the callback constructor to assign a name to a particular callback. If you do so, the results will become an object, with keys corresponding to the names you assigned.

Example

should = require 'should'
{focus} = require 'qi'

describe 'focus', ->
  it 'should wait for all callbacks to return', (done) ->
    cb = focus done

    setTimeout cb(), 1
    setTimeout cb(), 2
    setTimeout cb(), 3

  it 'should return all results', (done) ->
    cb = focus (err, results) ->
      should.not.exist err
      results.should.eql [0, 1]
      done()

    i = 0
    doStuff = (cb) ->
      -> cb null, i++

    setTimeout doStuff(cb()), 1
    setTimeout doStuff(cb()), 2

Disperse

This creates a function which when called will pass its args on to multiple child functions.

Example

should = require 'should'
{disperse} = require 'qi'

describe 'disperse', ->
  it 'should call all callbacks', ->

    yin = (input) ->
      input.should.eql 1

    yang = (input) ->
      input.should.eql 1

    taiji = disperse yin, yang
    taiji 1

Channel

This executes any number of tasks in sequence.

Example

should = require 'should'
{channel} = require 'qi'

describe 'channel', ->
  it 'should call multiple functions', (done) ->

    task1 = (arg, next) ->
      next null, arg * 4

    task2 = (arg, next) ->
      next null, arg + 2

    final = (err, arg) ->
      should.not.exist err
      should.exist arg
      arg.should.eql 42
      done()

    sequence = channel(task1, task2)
    sequence 10, final

FAQ

Q: Is focus safe to use on a mixture of synchronous and asynchronous subtasks?

A: Yes. Subtasks return their results on process.nextTick, so as long as you construct all your callbacks synchronously, your results should not be collected prematurely.

LICENSE

(MIT License)

Copyright (c) 2013 Torchlight Software info@torchlightsoftware.com

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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